Not applicable.
Not applicable.
1. Field of the Invention
The present invention is generally related to switches for use in optical fiber networks, and in particular provides an optical switch that switches an optical wedge in an optical signal path.
2. Background of the Invention
Optical fiber networks are used in a variety of applications, such as optical communication and data transmission systems. Optical fibers are generally very thin (e.g. 2-10 microns in diameter) glass fibers that have a core and a cladding that act as a waveguide for light signals. The light signals propagate down the fiber from one location to another, analogous to electrical signals traveling down a wire or cable from one location to another. However, light signals are different from electrical signals in a number of ways. For example, it is relatively simple to couple an electrical signal on one wire to another wire by simply joining the wires. Light signals traveling down an optical fiber, however, must be accurately directed or otherwise coupled to another fiber or device. Thus, switching light signals from one fiber to another frequently requires accurate mechanical alignment.
Several types of electromechanical switches have been developed to switch light signals from one fiber to another. One type of switch moves the ends of an input optical fiber relative to the ends of output optical fibers. Such methods rely on the accurate alignment of one fiber to another. However, the thin fibers are also delicate and subject to breakage if not reinforced, which adds undesirable stiffness to the fiber.
Another type of optical switch uses a mirror, such as a front-surface mirror or other reflective element, mounted on an arm or pole. The mirror is moved into and out of a light signal path from an input fiber. When the mirror is in the light signal path, it reflects the light signal to one output path, and when the mirror is removed from the light signal path, the light signal travels to another output path. Thus, optical switching is achieved by moving the mirror in and out of the light signal path, without moving the optical fibers. However, misalignment in the plane of the mirror typically results in a doubling of the error in the reflected beam. This not only necessitates precise alignment when the switch is assembled, but is also a consideration when designing the switch for shock load.
Additionally, in some configurations the beam is an arm moved by a relay. The arm is relatively long compared to either the dimensions of the mirror or the travel of the mirror, and it is generally desirable to keep the mass of the arm and mirror assembly low to facilitate the mechanical operation of the switch. Unfortunately, a lightweight arm is generally not as strong or as stiff as a heavier arm of similar materials and construction. If the switch is subjected to vibration that causes the mirror to rotate with respect to the input light beam, it is possible that the output beam from the mirror is moving twice the rotational angle of the mirror. A similar problem can arise from mechanical, thermal, or other distortions of the placement of the mirror.
Thus, it is desirable to provide an optical switch that is easier to align during fabrication, is more environmentally stable, less susceptible to shock and vibration, and is more reliable than conventional switches. It is also desirable that the optical switch be compact, and switch the light signal from one path to another with minimal signal loss.
The present invention provides improved optical switches with reduced sensitivity to linear and angular misalignment, shock, and vibration. A refractive, rather than reflective, optical element is switched between positions in a light signal path. The refractive optical element could be an optical wedge, for example, with two regions, each with different refractive properties. The switched optical wedge element produces less undesired deflection of the light beam resulting from shock, vibration, or misalignment compared to a reflective element, such as a mirror, particularly in a rotation of the element with respect to the incident light beam. Collimating lenses are typically used to expand the light signal from an input fiber, and to focus the light signal onto the end of an output signal fiber. xe2x80x9cInputxe2x80x9d and xe2x80x9coutputxe2x80x9d are used as terms of convenience for purposes of illustration only, those skilled in the art will appreciate the reciprocal nature of the optical switches.
In a particular embodiment an optical wedge is mounted on a switch mechanism, such as a hinged or elastic beam, armature, or slide, that is moved by an actuator, such as a solenoid, piezoelectric device, or other transducer. The optic wedge is mounted so that a face of the optic wedge is essentially normal to a light signal from an optical input. A second face of the optic wedge has a first portion that is essentially parallel to the first face, and a second portion that is angled to the first face, i.e. not parallel. In a first switch position, the light signal passes through the first face and the first portion of the second face to be transmitted with refraction of essentially zero degrees. In the second switch position, the light signal passes through the first face and the second portion of the second face to be refracted in a selected direction. Thus, the switch can direct the light signal to a first output port in the first position and to a second output port in the second position.
In a further embodiment, a wavelength-selective filter is placed between the input and the refractive element. The filter transmits, or xe2x80x9cdropsxe2x80x9d, selected wavelength of the input light signal, typically one or more channels defined according to an optical network transmission protocol, and reflects the remainder of the input light signal to an optical waveguide, such as an optical fiber. Thus, this embodiment allows a selected channel(s) to be switched between outputs, for example. In yet a further embodiment, a second wavelength-selective filter is placed between the refractive element and the optical outputs. Another fiber provides a light signal to be added to the input light signal at the wavelengths of the dropped channel(s), thus providing an ADD/DROP function with high isolation when combined with the reflected portion of the input light signal. The use of a thin wedge can provide close proximity between an input and output flashlight, resulting in little walk-off between light beam paths and low insertion loss.